Why is my Sims 3 base game incompatible?

I lost my Ambitions disc, and my Late Night game was downloaded from Amazon. So I insert my Base Game into the drive, and the launcher says that the Base Game is incompatible with my Expansion Pack. It says to update it, but when I go to the update center, I can't update anything. Should I uninstall the Sims 3 and restart with the Base Game? Should I call EA? What should I do?